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Creating the premium blend

10th August January, 2007

Environmental concerns, the possibility of petroleum shortages, and price rises have persuaded many governments that biofuels should form part of their overall fuel strategy. The same environmental and economic benefits would accrue from selling 5% pure biofuels and 95% petroleum-based fuels as from selling 5% blends. But it is not really feasible to ensure that 5% of consumers have the right vehicles, domestic or process heating equipment to use pure biofuels in the areas where the producers make them available. It is much easier to blend fuel for the whole market, and it is also technically more desirable.

Ethanol

Between 1970 and 2000 the octane-booster tetra-ethyl-lead was phased out of petrol production in almost every country in the world. Since then the most common octane increasing additive has been MTBE (methyl tertiary butyl ether). Now this too is being banned in many areas following concern over levels of MTBE in groundwater. Ethanol is the preferred alternative, and blending ethanol into petrol is standard practice around the world. Ethanol can be derived from either petroleum or biological sources, but using bioethanol enables suppliers to meet their governments' requirements for biofuels without fundamentally changing their product.

Conventional petrol does not mix with water so any rainwater or condensed atmospheric water settles at the bottom of tanks, where it can remain safely until the tank is emptied for cleaning. This is not the case with bioethanol, which absorbs any water it comes into contact with. The only cure if this happens is to return the affected fuel to the refinery for re-processing. So putting an ethanol blended fuel into tanks is risky. Rather than try to keep water out of every stage in the supply chain, it is easier and more reliable to keep the ethanol in separate tanks, which are monitored for water content, and then blend it into the petrol in the loading bay.

Biodiesel

Pure biodiesel has high lubricity, a high cetane number, and a high flash point. Cetane numbers and flash points both refer to the combustion properties of a fuel. Cetane is a chemical which ignites spontaneously under relatively low pressure, it is assigned the number 100 and other fuels are judged against that yardstick. Normal diesel fuels have a cetane number between 40-46 and premium diesels vary between 45 and 50. Biodiesel has a cetane number of around 55, making it a very useful additive to improve a standard fuel to a premium grade.

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